linux-kernel - Re: [PATCH v2 5/7] virtio-mem: s390 support

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Message-ID: <ebce486f-71a0-4196-b52a-a61d0403e384@redhat.com>
Date: Mon, 14 Oct 2024 21:16:45 +0200
From: David Hildenbrand <david@...hat.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 linux-doc@...r.kernel.org, kvm@...r.kernel.org,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
 Cornelia Huck <cohuck@...hat.com>, Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>, Mario Casquero <mcasquer@...hat.com>
Subject: Re: [PATCH v2 5/7] virtio-mem: s390 support

On 14.10.24 20:48, Heiko Carstens wrote:
> On Mon, Oct 14, 2024 at 04:46:17PM +0200, David Hildenbrand wrote:
>> The special s390 kdump mode, whereby the 2nd kernel creates the ELF
>> core header, won't currently dump virtio-mem memory. The virtio-mem
>> driver has a special kdump mode, from where we can detect memory ranges
>> to dump. Based on this, support for dumping virtio-mem memory can be
>> added in the future fairly easily.
> 

Thanks for the review.

> Hm.. who will add this support? This looks like a showstopper to me.

The cover letter is clearer on that: "One remaining work item is kdump 
support for virtio-mem memory. This will be sent out separately once 
initial support landed."

I had a prototype, but need to spend some time to clean it up -- or find 
someone to hand it over to clean it up.

I have to chose wisely what I work on nowadays, and cannot spend that 
time if the basic support won't get ACKed.

> Who is supposed to debug crash dumps where memory parts are missing?

For many production use cases it certainly needs to exist.

But note that virtio-mem can be used with ZONE_MOVABLE, in which case 
mostly only user data (e.g., pagecache,anon) ends up on hotplugged 
memory, that would get excluded from makedumpfile in the default configs 
either way.

It's not uncommon to let kdump support be added later (e.g., AMD SNP 
variants).

-- 
Cheers,

David / dhildenb